You ignore the email because you have more important things to worry about.

Eight years later, you have a newer iPhone and a bigger competitor. Airbnb was the startup mentioned in that email, and it now has the ability to serve more customers a day than your nearly 100-year-old company.

"If you are Hilton, if you are Starwood, if you are Hyatt, you didn't see Airbnb coming because Airbnb had none of the characteristics of a traditional competitor," Mohamed El-Erian, Allianz's chief economic advisor, said to journalists Monday.

"What's amazing about Airbnb is that the disrupters never built a hotel," he said. "What they knew was three simple things."

Uber is another prime example. Suddenly, from seemingly nowhere, entrenched taxi companies across the nation have a huge competitor they weren't prepared for. This has led to legal battles for Uber as the incumbents fight back.

But it's not just Airbnb and Uber that used these three factors. Nearly every disruptive startup we're familiar with today used them, according to El-Erian.

Here's what they are:

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1. Existing assets that are underutilized

Have a car that sits around a lot without being used? You can rent it out to a startup to make a little money on the side.

What about an extra dress you only wore that one time? Or maybe you want to rent out your weekends doing odd jobs for people. All are possible with a startup looking to use existing assets to create extra value.

"This phenomenon, of being able to disrupt ... is going to grow," El-Erian said. "And it's going to change the demand and supply dynamics of many industries."

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2. Millennials wanting more control

Airbnb hosts with multiple listings, according to the New York Attorney General.
New York Attorney General

Hotel rooms are pretty standard. Across brands and locations, they often look the same.

But with Airbnb, you can book a studio apartment in a hip area of Brooklyn or a penthouse multibedroom apartment in the middle of Manhattan. If you're tired of the same boring hotel rooms that are nearly always located near a highway or an airport, then Airbnb can offer an attractive alternative.

Airbnb and other disrupters cater to "a generation that wants better control over their destiny," El-Erian said.

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3. Mobility and technology advances

Thomson Reuters

A lot of disruptive technology now is apps. These companies have servers, customer-support staff, and developers helping to make their apps work, but it's ultimately the technology living in your pocket that makes the companies possible.

Uber was able to disrupt the competitive taxi industry, Airbnb disrupted hospitality, Seamless disrupted food delivery, and all of them were made possible by the advances in smartphone technology.

"This phenomenon of being able to disrupt from another world is going to grow. And it's going to change the demand and supply dynamics of many industries," El-Erian said.

"Machine learning and artificial intelligence allows you to power up in a way that you thought unimaginable."